Cysteine reaction with carbon dioxide

Fig. 1.8 Asaccharolytic fermentation produces ammonia and short-chain fatty acids. This group of fermentations by oral bacteria utilizes proteins, which are converted to peptides and amino acids. The free amino acids are then deaminated to ammonia in a reaction that converts nicotinamide adenine dinucleotide (NAD) to NADH. For example, alanine is converted to pyruvate and ammonia. The pyruvate is reduced to lactate, and ammonium lactate is excreted into the environment. Unlike lactate from glucose, ammonium lactate is a neutral salt. The common end products in from plaque are ammonium acetate, ammonium propionate, and ammonium butyrate, ammonium salts of short chain fatty acids. For example, glycine is reduced to acetate and ammonia. Cysteine is reduced to propionate, hydrogen sulfide, and ammonia alanine to propionate, water, and ammonia and aspartate to propionate, carbon dioxide, and ammonia. Threonine is reduced to butyrate, water, and ammonia and glutamate is reduced to butyrate, carbon dioxide, and ammonia. Other amino acids are involved in more complicated metabolic reactions that give rise to these short-chain amino acids, sometimes with succinate, another common end product in plaque.

Decarboxylation of the newly added cysteine (Cys, C) residue utilizing pyruvate (CH3COCO2H), a cofactor with phosphopantothenoylcysteine decarboxylase (EC 4.1.1.36), generates carbon dioxide (CO2) and pantotheine phosphate. Finally,coenzyme A is formed by the reaction of the pantotheine phosphate with ATP in the presence of pantotheine phosphate adenylyltransferase (EC 2.7.7.3). Inorganic diphosphate is formed at the same time (Scheme 12.107). 

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